1. Field of the Invention
This invention relates to the field of anesthesia, and specifically relates to synergistic compositions and methods for enhancing the activity of and/or for prolonging the duration of action of a local anesthetic.
2. Description of the Related Art
Conventional methods of prolonging the duration of anesthesia during surgeries include higher doses, repetition of doses, and continuous administration. All of these methods, however, may cause severe toxic and other side effects in patients. In addition, these methods are not suitable for post-surgical outpatient pain management. Consequently, much research has been directed towards reducing the anesthetic dose and prolonging the duration of action.
For example, Chinese Pat. No. CN1382443A provides a blowfish toxin whose duration of analgesia can reach about 6 hours. However, the toxicity of the blowfish toxin is over 1000 times higher than that of sodium cyanide which limits its applicability. Chinese Pat. No. CN1065203A provides an anesthetic prepared by adding sodium bicarbonate to a mixture of 1% amethocaine and 2% lidocaine in the proportion of 2-5:10-20, to adjust its pH value to between 7 and 7.2. This formula allegedly prolongs the original anesthesia duration from 48 min to 67 min. Chinese Pat. No. CN1075081A provides a compound gel anesthetic which contains chlorhexidini hydrochloride, dicaine hydrochloride, etamsylate, carboxymethyl cellulose, liquid paraffin and gentamicin sulphate. This preparation allegedly prolongs the original anesthesia duration from about 115 min to about 156 min. However, the duration of anesthesia disclosed in these patents is still insufficient for large surgeries.
The development of compounds and methods for post-operative pain management has also attracted attention. For example, Liu Xiaohong, at the Department of Anesthesiology of Chongqing Qianjiang Development Zone Central Hospital has developed a method of epidural administration for post-operative analgesia. This method comprises injecting 5 mL 0.5% bupivacaine combined with 10 mg dexamethasone by epidural administration and increases the duration of anesthesia to about 11.5 hours.
Nevertheless, certain large surgeries, especially liposuction, requires anesthesia lasting for up to 3 days or longer. Accordingly, it is imperative to develop compositions and methods which can prolong the duration of anesthesia greatly enough to meet with the need of long term analgesia, so as to relieve pain and suffering of patients.